An air traffic controller sent a Glasgow plane to Cardiff after misreading small computer text at the new control centre at Swanwick in Hampshire, it has been reported.

According to confidential documents obtained by the magazine, Computer Weekly, the controller had difficulty distinguishing the codes for the two cities.

Another also reportedly misread the heights of planes and sent an aircraft into the wrong airspace.

These are the teething problems you expect with a new computer system - the trouble is most don't have responsibility for controlling aircraft in the skies

Karl ScheiderComputer Weekly

The problems are said to have arisen because of the small size of the text on computer screens at the £623m new centre.

The Civil Aviation Authority (CAA) and National Air Traffic Services (Nats) insist that safety has not been compromised - a claim backed by the air traffic controllers union, Prospect.

Testing on an improved display is due to begin shortly.

Computer Weekly claims Nats and the CAA told it that only a small number of controllers have had screen-reading difficulties and it was not a safety-related concern.

But in a confidential report by controllers seen by the magazine, the controllers themselves categorised the errors as safety-related issues.

In one report, a controller reported having had "great difficulty" seeing clearly EGPF (the location code for Glasgow) and EGFF (the location code for Cardiff).

Cancelled flights

The controller had initially treated the aircraft as if bound for Cardiff and then discovered it was headed for Glasgow.

Controllers put safety first, second, third and last

Iain FindlayProspect union

Computer Weekly editor Karl Scheider said: "These are the sort of teething problems you expect with a new computer system - the trouble is most don't have responsibility for controlling aircraft in the skies."

The magazine reported the Swanwick controllers had repeatedly misread the height displayed on a screen by thousands of feet.

One controller reportedly mixed up FL360 (36,000ft) with FL300 (30,000ft) as the displayed height of an aircraft on his screen.

The report added the controller had been "repeatedly misreading" requested flight levels.

A further warning report said a controller misread a requested aircraft height level on an electronic flight strip and "co-ordinated the aircraft into the incorrect sector".

The mistake was spotted by another controller and corrected.

Radar screen

Iain Findlay of the air traffic controllers union Prospect, said safety had not been jeopardised as the problem did not affect the main control screens.

"It has to be made clear that there are two screens we are talking about.

"One is the planning screen where there are problems with the font size and the typeface - but that's not the screen that controls the aircraft.

"The radar screen has all the information and is reading properly."

He added: "We take safety very seriously indeed... controllers put safety first, second, third and last."

Computer problems at Swanwick delayed the opening of the new centre from 1996 to January of this year.

Another computer problem at the centre caused many flights to be cancelled or delayed last weekend.

On Tuesday, the CAA refused to allow the cash-strapped Nats to raise the charges it imposes on airlines.